Login / Registration -- openID ?? OAuth?? none??
None, as I don't depend much on third party

Voting -- keeping in mind this would require some auth
Allow only registered users to upvote down vote. Now am not sure about envy votes or bulk votes, which should be reversed in some way for sure but doesn't matter much

Comments -- again auth... I'm seeing a pattern here
No disqus, only registered users can comment, there should be limit to this of course

Licensing, if any. (is there a WTFPL for images?)
No Idea... but you need to get rid of the images uploaded by others if they you get a valid take down req, also you should warn the user if his image is deleted cuz of copyright issues which further should ban his account

Uploading -- drag and drop ofc, but I would also like to accept zip packages and unpack them on the server?? anything else about uploading on current sites you hate?
I think you should allow zips, sometime user want to upload icon packs, which may be in bulk so uploading in a single zip file will be preferable... but again, extensions will cause an issue here, so you need to handle that well...

Searching -- I'm going to try to bug a friend to show me how to do this based on image content and not just tags (skynet!).
display... I fucking hate the continuous scroll websites. that is a huge no go for me. other ideas welcome.

pagination....